Lightguide design techniques

ABSTRACT

Techniques are disclosed for obtaining a desired luminance and/or intensity distribution from any lighting fixture that is illuminated by a lightguide. The techniques can be used, for instance, to design a non-uniform surface texture (e.g., of light extraction features) for a lightguide, wherein the surface texture achieves a desired uniform or an intentionally non-uniform luminance distribution for a given lightguide shape/geometry, dimensions, and/or composition. In some embodiments, an iteration algorithm with illuminance distribution feedback is utilized to design a non-uniform surface texture (e.g., geometry, dimensions, quantity and/or spatial distribution of light extraction features) to achieve the target luminance distribution for a given lighting application.

FIELD OF THE DISCLOSURE

The invention relates to lightguide design techniques and resultinglighting fixtures.

BACKGROUND

Light emitting diode (LED)-based lighting design involves a number ofnon-trivial challenges, and edge-lit LED fixtures have faced particularcomplications, such as those with respect to achieving and/ormaintaining suitable lit appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an example edge-lit panel/fixture.

FIG. 1B is a cross-section view of the edge-lit panel/fixture of FIG. 1Ataken along dashed line X-X therein.

FIG. 2A illustrates a schematic front view of an example 2 ft.×2 ft.edge-lit light emitting diode (LED) lighting panel utilizing alightguide.

FIG. 2B illustrates luminance uniformity for the example edge-lit LEDlighting panel of FIG. 2A.

FIG. 3 is a flow diagram illustrating an iteration algorithm fordesigning a specific non-uniform surface texture to achieve a desiredluminance distribution for a given lightguide in accordance with anembodiment of the present invention.

FIG. 4 is a perspective view of a lightguide configured with anon-uniform distribution of light extraction features in accordance withan embodiment of the present invention.

FIG. 5A is a simulated two-dimensional mapping of surface illuminance ofa lightguide configured with a non-uniform distribution of lightextraction features in accordance with an embodiment of the presentinvention.

FIG. 5B is a current slice graph showing illuminance as a function oflocation along the X-direction of the simulated two-dimensional mappingof FIG. 5A.

FIG. 5C is a current slice graph showing illuminance as a function oflocation along the Y-direction of the simulated two-dimensional mappingof FIG. 5A.

The accompanying drawings are not intended to be drawn to scale.

DETAILED DESCRIPTION

Techniques are disclosed for obtaining a desired luminance and/orintensity distribution from any lighting fixture that is illuminated bya lightguide. The techniques can be used, for instance, to design anon-uniform surface texture (e.g., of light extraction features) for alightguide, wherein the surface texture achieves a desired uniform or anintentionally non-uniform luminance distribution for a given lightguideshape/geometry, dimensions, and/or composition. In some embodiments, aniteration algorithm with illuminance distribution feedback is utilizedto design a non-uniform surface texture (e.g., geometry, dimensions,quantity and/or spatial distribution of light extraction features) toachieve the target luminance distribution for a given lightingapplication. The resultant fixtures have a broad range of applications,such as in office lighting, commercial lighting, signage lighting,and/or display backlighting applications, and may exhibit relativelyhigh optical efficiency. Numerous configurations and variations will beapparent in light of this disclosure.

General Overview

FIG. 1A is a perspective view of an example edge-lit panel/fixture 100,and FIG. 1B is a cross-section view of the edge-lit panel/fixture 100 ofFIG. 1A taken along dashed line X-X therein. As can be seen, the exampleedge-lit panel/fixture 100 comprises a lightguide 110, an optionallyincluded back reflector 120 disposed proximate back surface 114 oflightguide 110, and one or more LED light sources 130 operativelycoupled to an input surface 112 of lightguide 110. In some cases,lightguide 110 may have on one or more of its surfaces (e.g., backsurface 114 and/or output surface 116) a surface texture formed by aplurality of light extraction features 140 (e.g., structures/materialsconfigured to reflect, refract, absorb, etc., incident light). As willbe appreciated in light of this disclosure, a given edge-litpanel/fixture 100 may include additional, fewer, and/or differentelements or components from those here described (e.g., diffusers,brightness enhancement films, polarizers, etc.), and the claimedinvention is not intended to be limited to implementation with anyparticular edge-lit panel/fixture configurations, but can be used withnumerous configurations in numerous applications.

Lightguide 110 may comprise an optical material chosen, at least inpart, based on its ability to: (1) be configured for total internalreflection (TIR) of at least a portion of the light provided by the oneor more LED light sources 130; and/or (2) transmit/emit thewavelength(s) of interest (e.g., visible, ultraviolet, infrared, etc.)of the light provided by the one or more LED light sources 130. Forexample, lightguide 110 may comprise a material such as, but not limitedto: (1) a transparent polymer such as poly(methyl methacrylate) (PMMA),polycarbonate, etc.; (2) a transparent ceramic such as sapphire (Al₂O₃),yttrium aluminum garnet (YAG), etc.; and/or (3) a transparent glass.Also, in some cases, lightguide 110 optionally may have one or moreoptical and/or protective coatings (e.g., anti-reflective; diffractive;etc.) disposed thereon.

The geometry of lightguide 110 may be customized for a givenapplication; for example, lightguide 110 may be configured as: (1) aplanar structure (e.g., a square/rectangular plate, a circular plate, anelliptical plate, etc.); (2) a curved/non-planar structure (e.g., athree-dimensional structure having at least one curved/non-planarsurface); and/or (3) any other lightguide configuration/structure. Inthe specific example case depicted in FIGS. 1A and 1B, lightguide 110 issubstantially configured as a square/rectangular plate having, amongothers, an input surface 112, a back surface 114, and an output surface116. Furthermore, the dimensions (e.g., length, width, height, etc.) oflightguide 110 may be customized for a given application. For instance,in one specific example case, lightguide 110 may be dimensioned forimplementation within a 2 ft.×2 ft. edge-lit panel/fixture 100, while inother example cases, lightguide 110 may be configured for implementationin edge-lit panels/fixtures 100 of smaller or larger area (e.g., in therange of a few micrometers to hundreds of meters or greater). Othersuitable configurations and/or materials for lightguide 110 will dependon a given application and will be apparent in light of this disclosure.

Light may be extracted (e.g., by the one or more light extractionfeatures 140, discussed in detail below) from lightguide 110 anddirected towards/through: (1) output surface 116; and/or (2) backsurface 114. As will be appreciated, permitting light to be extractedand emitted through back surface 114 may be undesirable for someapplications (e.g., ceiling lighting applications). In such cases, aback reflector 120 can be used to reflect/redirect at least a portion(e.g., substantially all) of the extracted light (e.g., which otherwisewould escape lightguide 110 through back surface 114 if not for backreflector 120) back towards/through output surface 116. Therefore,substantially all of the extracted light, regardless of initialdirection of extraction by light extraction features 140, may be made topass through output surface 116 of lightguide 110. When included, it maybe desirable to ensure that back reflector 120 is implementedsufficiently proximate to back surface 114 (e.g., such that the gapthere between is in the range of a few micrometers to a few millimeters)to ensure a sufficient amount of reflection. However, as will beappreciated in light of this disclosure, there may be some cases inwhich it is desirable to permit light to be extracted and emitted, forexample, through both of back surface 114 and output surface 116, and soback reflector 120 accordingly may be omitted from edge-litpanel/fixture 100.

Back reflector 120 may comprise, for example, a highly reflective metalfilm/layer such as aluminum, gold, silver, etc., that is chosen, atleast in part, based on its ability to reflect the wavelength(s) ofinterest of the light (e.g., visible, ultraviolet, infrared, etc.)provided by the one or more LED light sources 130. Also, much like withlightguide 110, the configuration of back reflector 120 may becustomized for a given application. For example, back reflector 120 maybe configured to conform to the shape of or otherwise complement: (1) aplanar structure (e.g., a square/rectangular plate, a circular plate, anelliptical plate, etc.); (2) a curved/non-planar structure (e.g., athree-dimensional structure having at least one curved/non-planarsurface); and/or (3) any other lightguide configuration/structure.

To this end, further note that the dimensions (e.g., length, width,height, thickness, etc.) of back reflector 120, when included, may becustomized for a given application. For instance, in one specificexample case, back reflector 120 may be dimensioned, like lightguide110, for implementation in a 2 ft.×2 ft. edge-lit panel/fixture 100,while in other example cases, back reflector 120 may be configured forimplementation in edge-lit panels/fixtures 100 of smaller or larger area(e.g., in the range of a few micrometers to hundreds of meters orgreater). In some cases, back reflector 120 may be dimensioned similarlyto back surface 114 (e.g., substantially similar/identical areas at theinterface between back surface 114 and back reflector 120) to ensurethat a minimal amount of light (e.g., substantially no light or anotherwise acceptable amount) escapes through back surface 114. Othersuitable configurations and/or materials for back reflector 120 willdepend on a given application and will be apparent in light of thisdisclosure.

As can further be seen, edge-lit panel/fixture 100 may include one ormore LED light sources 130 configured, for example, to deliver/emitlight into lightguide 110 (e.g., from input surface 112 thereof). Insome cases, the one or more LED light sources 130 may be: (1) physicallycoupled, for example, with input surface 112; and/or (2) disposedproximate to, but separate from, for example, input surface 112. The oneor more LED light sources 130 may be of any type (e.g., surfaceemitting, color independent, etc.), dimensions (e.g., greater than orequal to about 0.001 mm), and/or spectral emission band (e.g., visiblespectral band, infrared spectral band, ultraviolet spectral band, etc.)suitable for a given application. Other suitable configurations for theone or more LED light sources 130 will depend on a given application andwill be apparent in light of this disclosure.

As previously discussed, lightguide 110 may implement on one or more ofits surfaces (e.g., back surface 114 and/or output surface 116) asurface texture (e.g., a pattern/distribution of light extractionfeatures 140) which is configured to extract light from withinlightguide 110 (e.g., such as by reflection, refraction, absorption,etc.). In some instances, one or more light extraction features 140 maycomprise, for example, a substantially two-dimensional feature, such asa dot or other quantity of material (e.g., a reflective paint, aphosphor, a liquid such as oil or water, etc.). In some other instances,one or more light extraction features 140 may comprise, for example, athree-dimensional feature, such as, but not limited to: (1) a structurecomprising a material of different refractive index from that oflightguide 110 (e.g., a ceramic, a metal, air, etc.); (2) a formation ina surface of lightguide 110 (e.g., a void, vacuum, hole, hollow,depression, etc., formed within a given surface of lightguide 110);and/or (3) a formation on a surface of lightguide 110 (e.g., a bump,protrusion, projection, etc., formed on a given surface of lightguide110). In some cases, a given three-dimensional light extraction feature140 may be configured with a geometry, for example, like that of asphere, cylinder, cone, conical frustum, pyramid, pyramidal frustum,polyhedron, etc. For a given surface (e.g., back surface 114, outputsurface 116, etc.), light extraction features 140 may be internal and/orexternal to the confines/volume of lightguide 110.

As will be appreciated in light of this disclosure, light provided bythe one or more LED light sources 130 is coupled into lightguide 110,within which the light may reflect several times due to TIR, until it isincident to and extracted by one or more of the light extractionfeatures 140. As can be seen with particular reference to FIG. 1B, lightwhich is incident to a given light extraction feature 140 may beredirected, for example, towards output surface 116 and/or towards backsurface 114 (e.g., in which case a back reflector 120, if implemented,may reflect/redirect the light back towards output surface 116, aspreviously discussed).

However, as will be appreciated in light of this disclosure, traditionalapproaches to lightguide surface texture design (e.g., a simple uniformand/or linear pattern/distribution of light extraction features 140) donot provide a sufficiently uniform luminance distribution and/or colordistribution for use, for example, in most lighting applications (e.g.,office lighting, commercial lighting, signage lighting, displaybacklighting, etc.). This may be, at least in part, because the lightintensity provided by LED light sources 130 is typically non-uniform andnon-linear.

Furthermore, as previously indicated, there are a number of non-trivialissues that can arise which complicate obtaining and maintaining a goodlit appearance (uniform luminance and color distribution), for example,in lighting panels/fixtures. For instance, consider a 2 ft.×2 ft.edge-lit LED lighting panel/fixture which, in an attempt to obtainuniform luminance and color distribution, normally would require a highLED density (e.g., greater than or equal to about 100 OSLON LEDs for the2 ft.×2 ft. fixture/panel) or a large color mixing chamber in the lightengine design. However, these design approaches tend to increase systemcost and/or restrict the mechanical design of the lightingpanel/fixture.

There exist a number of techniques/designs which can be implemented inan attempt to obtain a degree of uniform luminance distribution forlarge edge-lit LED-based lighting fixtures, but these techniques aregenerally inadequate for various applications. For instance, somecommercially available software/programs (e.g., the Backlight PatternOptimization, or BPO, module of LightTools® from Synopsys, Inc.) may beutilized, for example, to design micro-feature distributions forlightguides for backlights. However, the optimization capabilities ofsuch software/programs are intrinsically limited due to the very largeparameter space attendant such designs (e.g., micro-feature size, shape,type, etc.). Furthermore, while such programs/software may provideacceptable optimization results when the initial values are similar tothe optimized values for relatively simple target functions, non-uniformluminance distribution implicates more complicated target functionswhich are difficult/impossible to define in such programs/software.

Also, there exist some algorithms which achieve uniform luminance forLCD and LED TV backlights, including: (1) trial and error (hardprototyping); (2) Fuzzy logic; (3) regional partition approach; (4)genetic algorithms; (5) neural network; and (6) molecular dynamics.However, while these algorithms may provide suitable uniformity in thespecific context of LCD and LED TV backlights, their low opticalefficiencies (40-65%) are unacceptable for lighting applications.Another existing approach involves implementation of diffusers toimprove uniformity of luminance distribution. However, such diffusiontechniques inherently reduce optical efficiency, which make theirimplementation unattractive for lighting applications.

There exist some edge-lit LED lighting panel/fixture products thatutilize non-uniform surface textures originally designed specificallyfor display or LCD TV backlights in an attempt to provide suitablyuniform luminance distribution for lighting applications. For example,consider FIG. 2A, which illustrates a schematic front view of an example2 ft.×2 ft. edge-lit LED lighting panel utilizing a lightguide designedby Global Lighting Technologies, Inc. As can be seen from FIG. 2B, whichillustrates luminance uniformity for the example edge-lit LED lightingpanel of FIG. 2A, the optical efficiency thereof is less than 64% andthe luminance uniformity thereof is less than 65%, as determined, forexample, by a 9-point uniformity test (e.g., 10% from the edge and themiddle point) based on 25 locations measured and interpolation. Aspreviously noted, such low optical efficiency is generally unacceptablefor lighting applications.

Therefore, there is need for a way of obtaining a suitably uniformluminance distribution, for example, in an edge-lit LED-based lightingfixture/panel, while achieving sufficiently high optical efficiency,minimizing/eliminating mechanical design constraints, and/or minimizingcost.

Thus, and in accordance with an embodiment of the present invention,techniques are disclosed for obtaining a desired luminance distributionfrom any edge-lit LED-based lighting panel/fixture (e.g., edge-litpanel/fixture 100) that is illuminated by a lightguide (e.g., lightguide110) having a surface texture comprising a plurality of light extractionfeatures (e.g., light extraction features 140) on one or more of itssurfaces (e.g., back surface 114 and/or output surface 116). As will beappreciated in light of this disclosure, and in accordance with anembodiment, techniques disclosed herein may be implemented to provide aspatially non-uniform surface texture of light extraction features 140on an internal and/or external surface (e.g., the inside and/or theoutside of back surface 114 and/or output surface 116) of a lightguide(e.g., lightguide 110), wherein the spatially non-uniform surfacetexture balances the non-uniform light intensity provided by the one ormore LED light sources 130 to achieve a desired luminance distribution,which may be uniform or intentionally non-uniform.

A surface texture configured in accordance with an embodiment of thepresent invention can be implemented with any given plurality of lightextraction features 140 regardless of their dimensions (e.g., greaterthan or equal to about 2 μm), geometry (e.g., two-dimensional and/orthree-dimensional), and quantity. Also, such a surface texture can beimplemented regardless of the type/configuration of the one or more LEDlight sources 130, of the shape/geometry (e.g., rectangular, square,circular, elliptical, planar, non-planar, curved, three-dimensional,etc.) and dimensions (e.g., having dimensions on the order of a fewmicrometers to hundreds of meters or greater) of lightguide 110, and ofwhether a back reflector 120 is optionally included.

An iteration algorithm is disclosed which, in accordance with anembodiment, can be used to design a surface texture (e.g., aconfiguration of light extraction features 140) for a given lightguide110 which achieves, as desired: (1) a uniform luminance distributionfrom a lightguide 110; and/or (2) an intentionally non-uniform luminancedistribution from a lightguide 110. Furthermore, in accordance with anembodiment, results generated by the iteration algorithm can beinterpreted to determine whether and/or how to adjust a given surfacetexture to achieve the desired luminance distribution. For instance, toachieve a desired luminance distribution, changes may be made to one ormore of the following variables associated with the light extractionfeatures 140 comprising the surface texture: (1) feature distribution(e.g., density, pattern/periodicity, etc.); (2) feature geometry (e.g.,shape, radius, angle, etc.); (3) feature size; (4) featurematerial/composition; and/or (5) any other feature parameters whichaffect light extraction. Thus, in some embodiments, the disclosediteration algorithm can be used with luminance distribution feedback todesign a lightguide 110 surface texture optimized for a given set of:(1) design constraints (e.g., componentry parameters for lightguide 110,back reflector 120, LED light sources 130, etc.); and/or (2)application/end use parameters (e.g., location, orientation, photometriccriteria, performance requirements, etc.).

Furthermore, as will be appreciated in light of this disclosure, thedisclosed iteration algorithm is not intended to be limited for use onlywith luminance feedback and adjustments. For instance, and in accordancewith an embodiment, iteration feedback may be provided by a wide varietyof light distribution parameters including, but not limited to, one or acombination of spatial distribution and/or angular distribution, forexample, of luminance, illuminance, luminous intensity, color, colortemperature, color rendering index (CRI), or other light properties, atnear-field and/or far-field. Adjustments to one or more of suchcharacteristics may be made, in accordance with an embodiment, asdesired for a given application.

As previously noted, some embodiments of the present invention may beimplemented, for example, to produce a lighting fixture having a desireduniform and/or intentionally non-uniform luminance distribution from agiven lightguide 110 configured with light extraction features 140 onone or more of its back surface 114 and/or output surface 116. However,the claimed invention is not so limited; for instance, some embodimentsof the present invention may be implemented, for example: (1) to obtainone or more non-emitting regions on an output surface 116 and/or a backsurface 114 of a lightguide 110; (2) to obtain color spatialdistributions on an output surface 116 and/or a back surface 114 of alightguide 110; and/or (3) to reduce glare exhibited by an edge-litpanel 100 by creating a gradual luminance transition in its lightguide110, for instance, from a bright light source to a dark background.

Some embodiments may be implemented to design surface textures of lightextraction features 140 for lightguides 110 customized for a givenapplication or end use based on: (1) design constraints (e.g., size,weight, heat output, etc.); and/or (2) photometric criteria (e.g.,luminous flux, luminous intensity, illuminance, luminance, etc.). Thus,as will be appreciated in light of this disclosure, one or moreembodiments of the present invention may be implemented, for example, todesign a highly efficient edge-lit LED lighting fixture/panel whichexhibits a suitable lit appearance (e.g., uniform/non-uniform luminanceand color distribution) for a wide range of applications such as, butnot limited to, office lighting, commercial lighting, signage lighting,and display backlighting. Other suitable uses will be apparent in lightof this disclosure.

As will further be appreciated in light of this disclosure, someembodiments of the present invention may provide advantages/benefitssuch as, but not limited to: (1) an improvement in luminance and coloruniformity (e.g., luminance and color distribution uniformity of greaterthan 65%; greater than 70%; greater than 75%; greater than 80%; etc.) ascompared with conventional techniques, designs, and products; (2) highoptical efficiency (e.g., greater than 65%; greater than 70%; greaterthan 75%; greater than 80%; greater than 85%; etc.) for various lightingapplications (e.g., office lighting, commercial lighting, signagelighting, display backlighting, etc.); and/or (3) high system efficacy(e.g., in the range of about 100 LPW at steady state for a 2 ft.×2 ft.lighting fixture/panel).

Furthermore, some embodiments may be implemented to achieve a desiredluminance and color distribution while simultaneously: (1) minimizingthe total quantity of LED light sources 130 implemented to achieve thedesired luminance/color distribution; (2) minimizing or otherwisereducing any resultant detriment to the optical efficiency of a lightingfixture/panel 100 including a lightguide 110 which implements a surfacetexture configured in accordance with an embodiment of the presentinvention; and/or (3) reducing the cost associated with the design of agiven lighting fixture/panel 100. Other advantages/benefits of variousembodiments of the present invention will be apparent in light of thisdisclosure.

Methodology

FIG. 3 is a flow diagram illustrating an iteration algorithm fordesigning a specific non-uniform surface texture to achieve a desiredluminance distribution for a given lightguide 110 in accordance with anembodiment of the present invention. The iteration algorithm of FIG. 3may be implemented, for example, to customize a given lightguide 110surface texture to achieve a desired uniform and/or intentionallynon-uniform luminance distribution in a single dimension and/or inmultiple dimensions (e.g., two or more dimensions simultaneously).Furthermore, as will be appreciated in light of this disclosure, and inaccordance with an embodiment, the disclosed algorithm can beimplemented with any given lightguide 110 independently of how LED lightsources 130 are operatively coupled therewith. For example, thedisclosed techniques can be implemented with: (1) edge-lit lightguides110 (e.g., LED light sources 130 are on an edge/side of lightguide 110);(2) bottom-lit lightguides 110 (e.g., LED light sources 130 are on thebottom of lightguide 110 and configured to couple light therein by areflector); and/or (3) hybrid lightguides (e.g., LED light sources 130are embedded into lightguide 110 and configured to couple light directlytherein). Numerous suitable lightguide implementations can be used inconjunction with the disclosed iteration algorithm, as will be apparentin light of this disclosure.

Turning now to the algorithm of FIG. 3, as in block 301, the lightguidesurface is divided into a plurality of zones (from 1 to n). In somecases, such division may be performed assuming that the lightguidesurface initially has: (1) a spatially uniform surface texture (e.g.,all zones from zone 1 to zone n have equivalent light extraction featuredensity); or (2) a spatially non-uniform surface texture (e.g., not allzones from zone 1 to zone n are of equivalent light extraction featuredensity). Thereafter, as in block 302, the luminance distribution iscalculated for each of the resultant zones (e.g., from zones 1 to n).

Next, beginning with the first zone (i=1), as in block 303, thecalculated luminance distribution for zone 1 is compared against thetarget luminance density for zone 1, as in block 304. The targetluminance is defined as the ratio between the design luminous flux of agiven zone and the total luminous flux of the entire lighting fixture.If the calculated luminance distribution for zone 1 is within anacceptable tolerance (e.g., ±10%, ±5%, ±2%, etc.) of the targetluminance density for zone 1, then keep/retain the surface texture ofthat zone 1 and proceed to block 306 of the algorithm. However, if thecalculated luminance distribution for zone 1 is not within an acceptabletolerance of the target luminance density for zone 1, then proceed toblock 305 of the algorithm and adjust the density of the lightextraction features within zone 1.

To this end, if the calculated luminance distribution for zone 1 is lessthan the target luminance density, then increase the density of lightextraction features within zone 1. Conversely, if the calculatedluminance distribution for zone 1 is greater than the target luminancedensity, then decrease the density of light extraction features withinzone 1. After making the appropriate adjustment to the density of lightextraction features within zone 1, return to block 302 and continue withthe algorithm.

Whenever a zone density is adjusted (e.g., increased or reduced), a newluminance calculation is needed until the luminance value for all zones1 to n meet the target luminance. Any time it is determined that thecalculated luminance distribution for a given zone is within anacceptable tolerance of the target luminance density for that zone, itshould be determined, as in block 306, whether the final zone n has beencompared. If the current zone is not the final zone n, then proceed asin block 307 with the next zone (i=i+1) and return to block 304 andsimilarly apply the algorithm as previously discussed above in thecontext of that new zone. Otherwise, if the current zone is the finalzone n, then the iteration algorithm may be terminated.

With regard to block 305, adjustments to the density of light extractionfeatures 140 of a given surface (e.g., back surface 114 and/or outputsurface 116) of lightguide 110 may be achieved by making changes to oneor more of a number of variables including, but not limited to: (1) thegeometry/shape of a given light extraction feature 140; (2) thedimensions of a given light extraction feature 140; (3) the totalquantity of light extraction features 140; and/or (4) the spatialdistribution of the light extraction features 140 on a given surface(e.g., back surface 114 and/or output surface 116) of lightguide 110. Aswill be appreciated in light of this disclosure, and in accordance withan embodiment, alteration/adjustment of one or more of such factors maybe performed to change the TIR conditions within lightguide 110 and thusachieve a desired uniform/non-uniform luminance distribution on a givensurface thereof (e.g., output surface 116). Other factors/parameters oflight extraction features 140 which may be tuned to achieve a desireduniform/non-uniform luminance distribution will depend on a givenapplication and will be apparent in light of this disclosure.

As will be appreciated in light of this disclosure, luminancedistribution for a given lightguide 110 may depend on a number offactors, including, but not limited to: (1) the type of LED light source130; (2) the coupling into lightguide 110 of the light provided by LEDlight source 130; (3) the geometry and/or structure of lightguide 110;and/or (4) the configuration of an optionally included back reflector120. Thus, as will further be appreciated in light of this disclosure, agiven lightguide surface texture which yields a suitable luminancedistribution in the context of one specific example application may notnecessarily function suitably for a different application when one ormore of such factors are changed. Therefore, in accordance with anembodiment, the iteration algorithm described herein can be implementedto individually refine/customize a given lightguide surface texture toachieve a desired luminance distribution specific to a given applicationor end use.

Numerous variations on this algorithm will be apparent in light of thisdisclosure. For instance, while the above algorithm is discussed interms of iterations based on luminance, the claimed invention is not solimited. In accordance with an embodiment, iteration feedback may beprovided by a wide variety of light distribution parameters including,but not limited to, one or a combination of spatial distribution and/orangular distribution, for example, of luminance, illuminance, luminousintensity, color, color temperature, color rendering index (CRI), orother light properties, at near-field and/or far-field.

As will be further appreciated in light of this disclosure, themultiple-zone representation can be made so as to, in one exampleembodiment, provide readily discernible zones of differing lightextraction pattern (e.g., such that a plurality of laterally and/orlongitudinally neighboring features in that zone are the same so as toprovide an overall two dimensional quality to the zone), while inanother example embodiment the multiple-zone representation may be madeto provide a continuously varying light extraction pattern (e.g., suchthat each feature is different from a laterally and/or longitudinallyneighboring feature so as to provide an overall one dimensional qualityto the zone). For example, with a relatively low quantity of zones(e.g., 2-20 zones), the configuration of light extraction features 140may have a coarser, step-like solution and the differences of each zonemay be more noticeable. Conversely, with a relatively high quantity ofzones (e.g., 21-200 zones, or greater), the configuration may have asmoother, more continuous solution and the differences of each zone maybe more subtle. In a more general sense, the number of zones does notprevent using a continuously varying light extraction pattern. Forinstance, one can use just one zone with varying light extractionpattern, to achieve a desired lighting result, wherein one or more lightextraction features within that zone are different from other featureswithin that zone. Whether a coarse, step-like solution or a fine,continuously changing solution, a plurality of zones having differinglight extraction features is provided. Further note that the lightextraction features need not be placed with any particular relationshipto one another. For instance, in one example embodiment, the lightextraction features can be formed in a grid pattern that has rows andcolumns of extraction features. Another embodiment may be configuredwith a more random or otherwise irregular placement of light extractionfeatures such that there are no consistent rows and/or columns. Inaddition, a zone may include any number of like light extractionfeatures (one or more like extraction features per zone) or a pluralityof two or more light extraction features that collectively are differentfrom the light extraction features of other zones, in some embodiments.For instance, in one embodiment, a first zone may have a single lightextraction feature of type A, and a second zone may have a plurality oflight extraction features of type B. In another embodiment, a first zonemay have light extraction feature types A and B, and a second zone mayhave light extraction feature types A and C. Any number ofconfigurations of differing light extraction feature types can be made.

In accordance with an embodiment, each of the functional boxes anddecision points shown in FIG. 3 can be implemented, for example, as amodule or sub-module that, when executed by one or more processors orotherwise operated, causes the associated functionality as describedherein to be carried out. The modules may be implemented, for instance,in software (e.g., executable instructions stored on one or morecomputer readable media), firmware (e.g., embedded routines of amicrocontroller), and/or hardware (e.g., gate level logic orpurpose-built silicon).

Example Structure and Simulated Implementation Data

FIG. 4 is a perspective view of a lightguide 110′ configured with anon-uniform distribution of light extraction features 140 in accordancewith an embodiment of the present invention. In some cases, thelightguide 110′ can be edge-lit, but other embodiments may have othersurfaces coupled to a light source, as will be appreciated in light ofthis disclosure. As can be seen, lightguide 110′ has been divided intoZones 1 through 8 (e.g., n=8). In this example case, each of Zones 1through 8 has an associated: (1) surface texture characteristic withrespect to, for example, composition, size, shape, and/or density oflight extraction features 140; (2) calculated luminance; and (3) targetluminance (e.g., defined as the ratio between the design luminous fluxof a given zone and the total luminous flux of the entire lightingfixture). As will be appreciated, some zones may have the same surfacetexture characteristic (light extraction features 140) as one or moreother zones, or all zones can be configured with different surfacetexture characteristics (light extraction features 140). Depending onthe application, some zones may not have any light extraction features140. In addition, each zone, or a sub-set of zones, may have lightextraction features 140 having, for example, a different composition,size, density, and/or shape relative to light extraction features 140 ofother zones.

For applications requiring, for example, a uniform luminancedistribution, the target luminance value may be 1/n of the lightingfixture's total luminous flux for all zones from 1 to n. For instance,if lightguide 110′ has 8 zones (n=8), then the target luminance value is⅛ for each of Zones 1 through 8. However, for applications requiring anon-uniform luminance distribution, the target luminance may bedifferent from the aforementioned 1/n distribution. For instance, ifthere are 8 zones (n=8), then the target luminance values for each ofZones 1 through 8 may be, for example,

$\frac{1}{32},\frac{1}{16},$⅛,

$\frac{9}{32},\frac{9}{32},$⅛,

$\frac{1}{16},{{and}\mspace{14mu}\frac{1}{32}},$respectively, of the lighting fixture's total luminous flux. As will beappreciated in light of this disclosure, these example target luminancevalues are included here for illustrative purposes only, and the claimedinvention is not intended to be limited to those example values. Othersuitable target luminance values for all zones from 1 to n will dependon the specifics of a given application.

FIG. 5A is a simulated two-dimensional mapping of surface illuminance ofa lightguide 110′ configured with a non-uniform distribution of lightextraction features in accordance with an embodiment of the presentinvention. FIG. 5B is a current slice graph showing illuminance as afunction of location along the X-direction of the simulatedtwo-dimensional mapping of FIG. 5A, and FIG. 5C is a current slice graphshowing illuminance as a function of location along the Y-direction ofthe simulated two-dimensional mapping of FIG. 5A.

The simulated data depicted in FIGS. 5A-5C effectively show that thedisclosed iteration algorithm may be implemented, in accordance with anembodiment, to produce a lightguide surface texture which achieves, asdesired, a luminance distribution (in one or more directions) having:(1) a high optical efficiency (e.g., about 65% or greater; about 70% orgreater; about 75% or greater; about 80% or greater; about 85% orgreater; etc.); and/or (2) high uniformity (e.g., about 65% or greater;about 70% or greater; about 75% or greater; about 80% or greater; etc.).While the example embodiment shown in FIGS. 5A-5C demonstratesachievement of a desired uniform/non-uniform luminance distribution, theclaimed invention is not so limited; for instance, as will beappreciated in light of this disclosure, and in accordance with anembodiment, techniques disclosed herein may be implemented to produce alightguide surface texture which achieves, as desired, a colordistribution (in one or more directions) having high optical efficiencyand/or high uniformity. As will further be appreciated in light of thisdisclosure, and in accordance with an embodiment, the observeddeviations in luminance distribution uniformity (e.g., seen asbright/hot spots in the upper left and right corners of the chart ofFIG. 5A) may be improved, for example, by implementing the iterationalgorithm in another direction (e.g., in the X-direction).

Numerous embodiments will be apparent in light of this disclosure. Oneexample embodiment of the present invention provides a lightguide deviceincluding an input surface configured to receive light from a lightsource and at least one surface having a surface texture comprising aplurality of light extraction features configured to direct incidentlight out of the lightguide device, wherein the surface texture isdivided into a plurality of zones including a first and a second zone,the first zone having light extraction features configured differentlythan light extraction features of the second zone, such that light isextracted from the first zone differently than from the second zone dueto the difference in their corresponding light extraction features. Insome cases, a density of the light extraction features of the first zoneis different than a density of the light extraction features of thesecond zone. In some other cases, a composition of the light extractionfeatures of the first zone is different from a composition of the lightextraction features of the second zone. In some other instances, thelight extraction features of the first zone are of a different size thanthe light extraction features of the second zone. In some cases, thelight extraction features of the first zone are of a different shapethan the light extraction features of the second zone. In someinstances, the lightguide further includes one or more additional zonesof light extraction features. In some such cases, each of the one ormore additional zones of light extraction features is configureduniquely with respect to the other zones. In some cases, the pluralityof zones provides a continuously varying light extraction pattern. Inother cases, the plurality of zones provides a stepped light extractionpattern. Other cases may include both a plurality of zones that providesa continuously varying light extraction pattern and a plurality of zonesthat provides a stepped light extraction pattern. Numerous suchvariations are possible.

Another example embodiment of the present invention provides a method ofdesigning a lightguide device, the method including dividing alightguide surface having an initial distribution of light extractionfeatures into a plurality of zones including a first and a second zoneand adjusting the light extraction features of the first zonedifferently than the light extraction features of the second zone, suchthat light will be extracted from the first zone differently than fromthe second zone due to the difference in their corresponding lightextraction features. In some cases, adjusting the light extractionfeatures of the first zone differently than the light extractionfeatures of the second zone includes calculating a light distributionparameter for the first zone, comparing the resultant calculated lightdistribution parameter for the first zone to a target light distributionparameter for the first zone, and adjusting the light extractionfeatures of the first zone until the light distribution parameter forthe first zone is within a given tolerance of the target lightdistribution parameter for the first zone. In some instances, the lightdistribution parameter comprises spatial and/or angular distribution ofat least one of luminance, illuminance, luminous intensity, color, colortemperature, and/or color rendering index (CRI). In some such cases, thelight distribution parameter for the first zone is different than alight distribution parameter for the second zone. In some other suchcases, adjusting the light extraction features of the first zonedifferently than the light extraction features of the second zonefurther includes increasing light extraction feature density for thefirst zone if the calculated light distribution parameter is lower thanthe target light distribution parameter for the first zone or decreasinglight extraction feature density for the first zone if the calculatedlight distribution parameter is higher than the target lightdistribution parameter for the first zone. In some other such cases, themethod further includes repeating the calculating, comparing, andadjusting for the second zone. In some instances, a density of the lightextraction features of the first zone is different than a density of thelight extraction features of the second zone. In some other instances, acomposition of the light extraction features of the first zone isdifferent than a composition of the light extraction features of thesecond zone. In some other instances, the light extraction features ofthe first zone are of a different size than the light extractionfeatures of the second zone. In some other cases, the light extractionfeatures of the first zone are of a different shape than the lightextraction features of the second zone. In some other cases, theplurality of zones further includes one or more additional zones oflight extraction features. In some such cases, each of the one or moreadditional zones of light extraction features is configured uniquelywith respect to the other zones. In some cases, the plurality of zonesprovides a continuously varying light extraction pattern (e.g., asopposed to a stepped light extraction pattern).

Yet another example embodiment of the present invention provides alighting device including one or more light sources configured to emitlight and a lightguide comprising an input surface configured to receivelight from the one or more light sources and at least one surface havinga surface texture comprising a plurality of light extraction featuresconfigured to direct incident light out of the lightguide, wherein thesurface texture is divided into a plurality of zones including a firstand a second zone, the first zone having light extraction featuresconfigured differently than light extraction features of the secondzone, such that light is extracted from the first zone differently thanfrom the second zone due to the difference in their corresponding lightextraction features. In some cases, the lighting device has an opticalefficiency of greater than or equal to about 80%. In some other cases,the lighting device further includes a back reflector operativelycoupled to the lightguide and configured to ensure that substantiallyall of the light received by the lightguide is directed out of a singleoutput surface of the lightguide. In some cases, the plurality of zonesprovides a continuously varying light extraction pattern.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A method of designing a lightguide devicecomprising: dividing a lightguide surface having an initial distributionof light extraction features into a plurality of zones including a firstand a second zone; and adjusting the light extraction features of thefirst zone differently than the light extraction features of the secondzone, such that light will be extracted from the first zone differentlythan from the second zone due to the difference in their correspondinglight extraction features.
 2. The method of claim 1, wherein adjustingthe light extraction features of the first zone differently than thelight extraction features of the second zone comprises: calculating alight distribution parameter for the first zone; comparing the resultantcalculated light distribution parameter for the first zone to a targetlight distribution parameter for the first zone; and adjusting the lightextraction features of the first zone until the light distributionparameter for the first zone is within a given tolerance of the targetlight distribution parameter for the first zone.
 3. The method of claim2, wherein the light distribution parameter comprises spatial and/orangular distribution of at least one of luminance, illuminance, luminousintensity, color, color temperature, and/or color rendering index (CRI).4. The method of claim 2, wherein the light distribution parameter forthe first zone is different than a light distribution parameter for thesecond zone.
 5. The method of claim 2, wherein adjusting the lightextraction features of the first zone differently than the lightextraction features of the second zone further comprises: increasinglight extraction feature density for the first zone if the calculatedlight distribution parameter is lower than the target light distributionparameter for the first zone; or decreasing light extraction featuredensity for the first zone if the calculated light distributionparameter is higher than the target light distribution parameter for thefirst zone.
 6. The method of claim 2 further comprising repeating thecalculating, comparing, and adjusting for the second zone.
 7. The methodof claim 1, wherein a density of the light extraction features of thefirst zone is different than a density of the light extraction featuresof the second zone.
 8. The method of claim 1, wherein a composition ofthe light extraction features of the first zone is different than acomposition of the light extraction features of the second zone.
 9. Themethod of claim 1, wherein the light extraction features of the firstzone are of a different size than the light extraction features of thesecond zone.
 10. The method of claim 1, wherein the light extractionfeatures of the first zone are of a different shape than the lightextraction features of the second zone.
 11. The method of claim 1,wherein the plurality of zones further comprises one or more additionalzones of light extraction features each of which is configured uniquelywith respect to the other zones.
 12. The method of claim 1, wherein theplurality of zones provides a continuously varying light extractionpattern.